Automotive weather-strip applications require a unique balance of properties to qualify as an acceptable product. A polymer formulation must have an excellent mixing rate (MR), and must produce a product with excellent mechanical properties. Formulations based on a unimodal (typically one polymer) EPDM polymer often have unacceptable mixing rates and/or form products with unacceptable mechanical properties. Formulations based on bimodal (two polymers) EPDM blends typically cannot be prepared reproducibly, and lead to additional variability in the polymer formulation and final article. There is a need for EPDM-based formulations that have excellent MR and scorch resistance values, and can be used to form automotive weather-strips with excellent mechanical properties. There is a further need for an EPDM composition that can be used in a free-flowing pellet form for both rapid mixing of the final polymer formulation and a high production rate of the formulation. There is a further need for a composition that can be pelletized for rapid mixing of the pellet in a rubber formulation, for a high production rate of the formulation, and to reduce the thermal history due to high temperature and high shear mixing of unpelletized forms of the formulation.
U.S. Pat. No. 7,199,189 discloses a polymer composition comprising a metallocene catalyzed reactor blend of: a) 10 to 30 weight percent semicrystalline minor component, having 65 to 75 weight percent ethylene derived units; 0 to 10 weight percent diene derived units; and alpha-olefin derived units having 3 to 10 carbon atoms making up the remainder of the minor component; and b) 70 to 90 weight percent amorphous major component, having 60 to 70 weight percent ethylene derived units; 0 to 10 weight percent diene derived units; and alpha olefin derived units having 3 to 10 carbon atoms making up the remainder of the major component. The viscosity of the major component is less than one fourth the viscosity of the minor component, and wherein the blend has a diene content of at least 0.5 weight percent based on the total weight of the blend. However, such blends have relatively high viscosity at high shear rates, and are more difficult to fabricate into parts with complex geometries.
U.S. Pat. No. 6,319,998 discloses a method of making polymer blends using series reactors and a metallocene catalyst. More specifically, this invention relates to making blends of EP (ethylene-propylene) copolymers, in which the blend components differ in any of the following characteristics: 1) composition 2) molecular weight, and 3) crystallinity. This reference discloses propylene-base polymers that typically have lower crosslinking efficiencies with peroxides.
U.S. Pat. No. 5,242,971 discloses ethylene-propylene-diene rubbers having a Mooney viscosity from 50 to 120, and comprising from 90 to 40 percent by weight of a high-molecular weight ethylene-propylene-diene copolymer rubber, having an ethylene content of 73 to 85 mol percent, an intrinsic viscosity [η] of 2.5 to 5.0 dl/g, as measured at 135° C. in decalin, and an iodine value of 15 to 35; and from 10 to 60 percent by weight of a low-molecular-weight ethylene-propylene-diene copolymer rubber, having an ethylene content of 73 to 85 mol percent, an intrinsic viscosity [η] of 0.15 to 0.8 dl/g, as measured at 135° C. in decalin, and an iodine value of 15 to 35. The components of the rubber are melt blended using temperatures up to 170° C. This significant thermal history causes less reproducibility in the rheological behavior and crosslinking behavior of the rubber.
U.S. Pat. No. 6,040,351 discloses compositions containing the following: (A) a low-molecular weight ethylene-propylene-5-ethylidene-2-norbornene terpolymer, having a Mooney viscosity from 20 to 40, an ethylene/propylene ratio by weight from 65/35 to 50/50, an iodine value from 20 to 30, and a Q value (Mw/Mn) not exceeding 3, as determined by gel permeation chromatography; (B) a high-molecular ethylene-propylene-5-ethylidene-2-norbornene terpolymer having a Mooney viscosity from 100 to 300, an ethylene/propylene ratio by weight from 65/35 to 50/50, an iodine value from 20 to 30, and a Q value (Mw/Mn) from 6 to 10; (C) a vulcanizing agent containing sulfur as a vulcanizer, and zinc carbamate and sulfenamide as accelerators; and (D) a foaming agent containing N,N′-dinitrosopentamethylenetetramine and urea. The components of the rubber are melt blended using temperatures up to 170° C. This significant thermal history induces a higher degree of variation in the rheological behavior and crosslinking behavior of the rubber. Also, the broader molecular weight distribution of the high molecular weight component will tend to lower the crosslinking efficiency of the rubber.
U.S. Pat. No. 5,973,017 discloses a foamed rubber blend comprising an EPDM blend, comprising at least one high molecular weight component and at least one low molecular weight component. The high molecular weight component has a weight average molecular weight (Mw) from 400,000 to 800,000, and a molecular weight distribution index (Mw/Mn) from 5.5 to 9.5. The low molecular weight component has a weight average molecular weight (Mw) from 150,000 to 500,000, and a molecular weight distribution index (Mw/Mn) from 1.5 to 5.5. The EPDM rubber has an overall weight average molecular weight (Mw) from 200,000 to 700,000. The ratio of the polymer blend in the foamed rubber blend is in a range of from 33 weight percent to 60 weight percent. The very high molecular weight component of the blend will tend to result in more limited processibility of the blend, and will reduce the crosslinking efficiency of the blend due to its broad molecular weight distribution.
U.S. Pat. No. 6,531,546 (see also EP 1186631A1) discloses a rubber composition comprising (a) a low molecular weight copolymer rubber, which is an ethylene/α-olefin/non-conjugated diene copolymer rubber having a limiting viscosity [η] of 0.4-1.6 dl/g, measured in decalin at 135° C., and an ethylene content of 40-60 weight percent; and (b) a high molecular weight copolymer rubber, which is an ethylene/α-olefin/non-conjugated diene copolymer rubber having a Mooney viscosity (ML 1+4, 100° C.) of 60-150, an ethylene content of 60-80 weight percent, and an iodine number of 5-35. The rubber composition has a Mooney viscosity (ML 1+4, 100° C.) of 20-50. These low viscosity blends would have limited oil extension and limited filler extension. The crosslinking efficiency would also be reduced. The ethylene/α-olefin/non-conjugated diene copolymer rubber having a limiting viscosity [η] of the above range of “0.4-1.6 dl/g” has a Mooney viscosity (ML1+4, 100° C.) of 19 or less. It is widely know that the measured Mooney viscosity of a polymer generally decreases with increase in measurement temperature. Thus, the Mooney viscosity of a polymer measured at 125° C. (ML1+4, 125° C.) is generally lower than the Mooney viscosity measured at 100° C. (ML1+4, 100° C.).
Additional EPDM blends and/or methods of preparing rubber blends are disclosed in U.S. Pat. No. 5,191,042; U.S. Pat. No. 5,229,478; U.S. Pat. No. 6,153,704; U.S. Pat. No. 6,329,477; and European Patent Application No. EP 0446380A1.
As discussed above, there remains a need for EPDM-based formulations that can be used to form weather-strips with excellent mechanical properties with a high degree of consistency. These formulations should be usable in free-flowing pellet form for both rapid mixing of the final polymer formulation and a high production rate of the formulation. These needs and others have been met by the following invention.